A technology for using a permanent magnet formed by cleaving and splitting so as to reduce a surface area in a rotor core of a rotating electrical machine is known. By forming the permanent magnet as above, an eddy current generated by fluctuation in a magnetic field is reduced. Then, heat generation of the permanent magnet caused by the eddy current is suppressed. As a result, irreversible thermal demagnetization can be prevented.
A method of cleaving a permanent magnet is described in JP2009-142081A. In this JP2009-142081A, the inside of a container having an inside hollow dimension and an inside hollow shape equal to a dimension and a shape of a rotor slot is used. First, a resin is filled in this container. Subsequently, a permanent magnet provided in advance with a notch which becomes a target of cleaving is inserted. Then, the permanent magnet is cleft in the container into magnet pieces. By cleaving the permanent magnet as above, the resin is infiltrated between the magnet pieces.